A salt bath is basically placing a fish into a smaller container with salted water for a period of time. It is supposed to be a way to medicate fish but IMO it is not a good option. Taking an already sick fish and exposing it to high levels of salt then removing it back to no or low levels of salt seems to me like it would be unnecessary stress.

Some people swear by them but IMO if you have a sick fish you should try to make its environment as stress-less as possible. I do salt my tanks when I have a sick or injured fish (only for 10 days at a time)... but I do it a little at a time, gradually raising the salt level over a few days and I do it in a permanent or semi-permanent (i.e. hospital tank) tank vs. a smallish cup or bowl.